1. Field of the Invention
The invention relates to a connection electrode connecting device having a plurality of opposing electrodes provided on a substrate surface, the connection electrodes being provided on approximately hemispherically shaped protrusions on a flexible substrate provided so as to face each of the opposing electrodes, and a support member which provides a pressing force from the rear of the protrusions.
2. Description of Related Art
This type of connection electrode connecting device is used in connections between flexible circuits and the heads of ink ejecting printers, such as is disclosed in U.S. Pat. No. 5,262,802.
With such an ink ejecting printer, a plurality of nozzles are provided on the head, and a heating resistor is provided in the back of each nozzle. If a predetermined current is supplied to the heating resistor when ink is supplied near each heating resistor, the ink near the heating resistors to which current has been supplied is heated to a boiling state, and is sprayed from the nozzles corresponding to the printing information.
Because the head is always moving, the supplying of electricity to each of the heating resistors is conducted by means of a flexible circuit which is composed of a semiconductor pattern formed on a pliable resin substrate. In addition, because it is necessary to change the heads each time all of the ink in the head has been consumed, the head is removably attached to a carriage. Furthermore, the supply of electricity to each of the heating resistors is conducted by causing contact between the opposing electrodes provided on the head surface and a connection electrode provided on the flexible circuit surface.
In addition, the connection electrode connecting device of this type of printer is disclosed in U.S. Pat. No. 4,706,097. With this type of connection electrode connecting device (FIG. 9), the resin substrate 14 of the flexible circuit 15 is raised from the substrate surface by the connection electrode 13 installation portion. The connection electrode 13 easily contacts the opposing electrodes 12 provided on the rigid substrate 11. On the other hand, a support plate (not shown) opposes the head (not shown) so that the flexible circuit 15 that is interposed therebetween is provided on the carriage (not shown). Rubber backup members 18 are formed on the support plate surface so that a backup member 18 contacts the resin substrate 14 from behind each of the connection electrodes 13. Through these backup members 18, the connection electrodes 13 and each of the opposing electrodes 12 are kept in a state of being pressed into contact with one another.
Each backup member 18 is composed of a conical portion 16 that contacts the resin substrate 14 and a cylindrical base portion 17. Because the conical portion 16 and the cylindrical base portion 17 are formed integrally of the same material (rubber), the spring constant of the conical portion 16, which has the shape of a cone, is smaller than the spring constant of the cylindrical base portion 17, which has the shape of a cylinder.
In a flexible circuit 15, such as described above, there are cases wherein a variance is created in the height to which the electrodes are raised from the surface of the resin substrate 14, such as is shown in FIG. 13, through the press process whereby the connection electrode 13 portion of the resin substrate 14 is caused to be raised. In such a case, when the connection electrodes 13 are caused to make contact with the opposing electrodes 12, the connection electrode 13B, which has a lower height than the surrounding connection electrodes 13, makes first contact with its backup member 18B and begins its compression process first.
Next, as shown in FIG. 14, the pressure necessary to deform the resin substrate 14 by the difference h in height of the adjacent connection electrodes 13 is applied to the backup member 18B, the conical portion 16B is compressed, and following this, as shown in FIG. 15, the connection electrodes 13A,13C which have taller heights, come into contact with the backup members 18A,18C, respectively, and compression in the backup members 18A, 18C is started. During this interval, the backup member 18B, which entered the compression process first, begins compression deformation first with the conical portion 16B while the pressing force of the connection electrode 13B is small because the conical portion 16B has a smaller spring constant than the cylindrical base portion 17. As the pressing force becomes larger, the compression deformation eventually moves to the cylindrical base portion 17B.
As shown in FIG. 10, when the conical portion 16 is compressionly deformed, the relationship between the spring force and the compression amount of the backup member 18, indicated by region A in FIG. 10, appears to be nonlinear. Further, when the cylindrical base portion 17 is compression deformed, the relationship between the spring force and the compression amount of the backup member 18, indicated by region B in FIG. 10, appears to be approximately linear. In other words, the spring force increases exponentially until a certain compression amount is reached, but when the compression amount exceeds this region or amount, the spring force increases linearly.
The relationship between the difference h in height of the connection electrodes 13 and the difference in pressing force on the connection electrodes 13 will now be described with reference to FIGS. 11 and 12. Graphs 10 and 12, in FIGS. 11 and 12, respectively, indicate the relationship between the spring force and the displacement of the backup member 18B, while graphs 11 and 13, in FIGS. 11 and 12, respectively, indicate the relationship between the spring force and the displacement of backup members 18A,18C.
First, when the displacement X1 of the backup member 18B, measured from where the backup member 18B contacts (L1) the connection electrode 13B having the shorter height to where the backup members 18A,18C contact (L2) the connection electrodes 13A,13C, respectively, having taller heights, is sufficiently smaller than the displacement of Y for the nonlinear elastic deformation region 10Y of the backup member 18B, the backup member 18B has obtained a displacement of X1+Z1 and the backup members 18A,18C have obtained a displacement of Z1, as shown in FIG. 11, at the time (L3) the head is mounted on the carriage. As can also be seen from FIG. 11, at the time (L3) when the head is mounted on the carriage, the spring forces of backup member 18B and of backup members 18A,18C are in the approximately linear deformation regions 10W and 11W, respectively. Consequently, the difference Q between the spring forces of backup member 18B and backup members 18A,18C is small, so the difference between the pressure on connection electrode 13B and the pressure on connection electrodes 13A,13C is also small.
However, when the difference h in height of the connection electrodes 13 is large and the displacement X2 of the backup member 18B, measured from where the backup member 18B contacts (L4) the connection electrode 13B having the shorter height to where the backup members 18A,18C contact (L5) the connection electrodes 13A,13C having taller heights, is larger than the displacement of Y for the nonlinear elastic deformation region 12Y of the backup member 18B, as shown in FIG. 12, the following problems arise. At the time (L6) when the head is mounted on the carriage, as shown in FIG. 12, the backup member 18B has obtained the displacement of X2+Z2 and the backup members 18A, 18C have obtained the displacement of Z2. As can also be seen from FIG. 12, at the time (L6) when the head is mounted on the carriage, the spring force B1 of backup member 18B is positioned in the approximately linear elastic deformation region 12W, while the spring force B2 of backup members 18A,18C is positioned in the nonlinear elastic deformation region 13Y. Consequently, the difference Q' between the spring force B1 of the connection electrode 13B having the shorter height and the spring forces B2 of the connection electrodes 13A,13C having taller heights becomes larger. That is to say, the pressing force on connection electrode 13B becomes very large with respect to the pressing force on connection electrodes 13A,13C. As a result, the pressing force on the connection electrodes 13A,13C, having taller heights is insufficient, creating the problem that it becomes impossible to obtain good electrical connections.